In the conventional boost PFC circuits, the bridge rectifier loss becomes one of the main losses of the switching power. Following the requirements regarding the convention efficiency are improved, the bridgeless boost topology deriving from the conventional boost PFC circuit has gradually become the focus of the R&D. The bridgeless boost topology omits the bridge rectifier of the boost PFC circuit so that there're only two diodes in the operational loop, which reduces a diode conducting loss, and increases the efficiency. H-PFC circuit belongs to a kind of bridgeless boost topologies suitable for the medium power and large power applications (please refer to FIG. 1). In FIG. 1, the bridgeless PFC circuit includes an inductor L, four diodes D1-D4, a bidirectional switch comprising two switches Q1-Q2, and an output capacitor CB, receives the AC input voltage Vin, and generates the DC output voltage Vo.
FIGS. 2(a)-2(b) are schematic circuit diagrams respectively showing the operational statuses of the positive half-cycle and the negative half-cycle of a period of operational frequency of the H-PFC circuit as shown in FIG. 1. The elements included in FIGS. 2(a)-2(b) are the same as those of FIG. 1, wherein the driving signals of the switches Q1 and Q2 have the same phase. In FIG. 2(a), L, D1, D4, Q 1, Q2 and CB form a boost circuit when the input voltage Vin is in its positive half-cycle, wherein D4 and Q2 are turned on continuously. The current flows through L, Q1 and Q2 and then returns when Q1 turns on. The current flows through L, D1, CB, and D4 and then returns when Q1 turns off. In FIG. 2(b), L, D2, Q1, Q2, D3 and CB form another boost circuit when the input voltage Vin is in its negative half-cycle, wherein Q1 and D3 are turned on continuously. The current flows through L, Q1 and Q2 and then returns when Q2 turns on. The current flows through L, D3, CB and D2 and then returns when Q2 turns off. The currents flow through L, Q1 and Q2 are respectively in reverse directions when they are in the positive and the negative half-cycles. Due to that D3 and D4 clamp the AC power source to the output capacitor CB of the boost circuit, a common mode noise, which is the same as the conventional boost PFC circuit, could be obtained. Since the current flows through only two semiconductor elements during any time in a switch period, the conduction loss is decreased.
Keeping the drawbacks of the related arts in mind, and employing experiments and research full-heartily and persistently, the applicants finally conceived a bridgeless power factor correction circuit system having a current sensing circuit and a controlling method thereof.